The invention relates to an implant to be surgically fitted in bone, preferably human bone, and covers for example the areas of osteosynthesis, prosthetics (in surgery of the hands, feet, hips and limbs), and maxillofacial and dental implantology. The invention in particular concerns the design of the implant and of its surface for the purpose of achieving immediate primary stability and rapid osseointegration.
There are two requirements regarding the stability of an implant:
a) an as far as possible immediate postoperative load-bearing capacity, i.e. immediate primary stability, which is based solely on mechanical principles; and
b) as rapid as possible secondary stability by means of osseointegration, which follows biological principles.
Apart from the quality of implantation and the local conditions in the area surrounding the implantation site, it has been recognized that a critical factor regarding the primary stability of the implant is its design, and that an outer screw thread delivers the best results for immediate stability. By contrast, osseointegration is crucially dependent on the choice of material (titanium and titanium-based alloys and porcelain-like substances are being increasingly used in this connection) and on the surface characteristics of the implant.
In GB-A-2,045,083, a surface roughness of the order of 0.01 xcexcm to 0.3 xcexcm is recommended. EP-B-0,388,576 proposes an ideal implant surface with a macro-roughness of more than 10 xcexcm, preferably more than 20 xcexcm, on which a micro-roughness of the order of 2 xcexcm and finer is superimposed. Treating the implant surface with an abrasive is proposed in order to generate the macro-roughness, and etching in acid is proposed in order to generate the micro-roughness. WO-A-97/28760 discloses, for osteosynthesis screws, a roughness value Rt of ca. xe2x89xa710 xcexcm (maximum peak-to-valley height). According to Schroeder, A.; Sutter, F.; Buser, D.; Krekeler, G. (Orale Implantologie [Oral implantology], Georg Thieme Verlag, Stuttgart, 2nd edition, 1994, pages 48 et seq.), a plasma coating with a layer thickness of ca. 20-40 xcexcm and a peak-to-valley height of ca. 15 xcexcm is applied to the implant surface in order to increase the surface and promote osseointegration. In general, specialists in this field are of the firm opinion that macro and micro roughnesses, particularly in combination, promote the anchoring of intraosseous implants in the bone.
U.S. Pat. No. 4,865,603 discloses prosthetic implants which have a surface with a structure. The structure comprises first and second depressions, the dimensions of the second depressions being in the range of 25% to 75% of the dimensions of the first depressions. The dimensions of the first depressions, in particular the width, are in the range of between 200 xcexcm and 1000 xcexcm, preferably between 300 xcexcm and 700 xcexcm, and consequently the dimensions of the second depressions lie in the range of 50 xcexcm to 750 xcexcm, preferably in the range of 75 xcexcm to 525 xcexcm. The depth of the first depressions and also of the second depressions lies in principle in the range of the dimension, in particular the width, of the respective depressions. The second depressions can be groove-shaped or diamond-shaped in configuration.
Although previous measures have brought some progress in terms of primary and secondary anchoring of intraosseous implants in bone implant sites, further improvements are nevertheless desired in order to increase the rate of success of the implants, shorten overall surgical procedure and thus impose less strain on the patient and ensure that the patient can return more quickly to a by and large normal lifestyle.
In view of the aims set out above, it is an object of the invention to create, for intraosseous implants, a surface structure which gives a high degree of primary stability immediately following surgery and which promotes rapid and as intensive as possible biological osseointegration of the fitted implant.
The main features of the invention can be summarized as follows:
The intraosseous implant intended to be fitted in a bone is provided with a specific roughness on the surface, said implant surface having a multiplicity of depressions with a vertically measured depth of 20 xcexcm to 60 xcexcm, between which there are plateau faces. At the bottom of the depressions there are base faces, and side faces extend from the base faces to the plateau faces. The base faces and the plateau faces have a horizontal extent of in each case 10 xcexcm to 20 xcexcm. The depressions and the plateau faces are smooth, i.e. they have no surface roughness which although below the cellular dimension of osteogenetic cells is nevertheless in the same order of magnitude.
The side faces of the depressions preferably form an angle of inclination relative to the horizontal of about 30xc2x0 maximum. The implant preferably has an upper neck portion, and below this upper neck portion, a self-tapping thread. The neck portion of the implant can be provided with a porcelain-like coating. The surface energy, or xe2x80x9czeta potentialxe2x80x9d, and the surface tension of the implant are kept preferably as low as possible. Materials used for the implants are preferably titanium, titanium-based alloys or porcelain-like substances. The depressions are preferably designed as systematically trapezoid grooves extending parallel to one another, said grooves being generated mechanically.
By virtue of the invention, an implant is now available which, while providing sound immediate postoperative primary stability, is distinguished, on account of improved osseointegration in terms of the biological union of the bone and the implant surface, by an accelerated and increased load-bearing capacity in terms of secondary anchoring.
The intraosseous implant intended to be fitted in a bone is provided with a specific roughness on the surface, where said implant surface:
a) has a multiplicity of depressions with a vertically measured depth of about 20 xcexcm to about 60 xcexcm;
b) at the bottom of the depressions there are base faces, and between the depressions there are plateau faces, said base faces and plateau faces having a horizontal extent of about 10 xcexcm to about 20 xcexcm;
c) side faces extend from the plateau faces to the base faces; and
d) the depressions and the plateau faces are ideally as smooth as possible, that is to say they have no surface roughness below the cellular dimension.
The side faces of the depressions form an angle of inclination relative to the horizontal of about 30xc2x0 maximum. Below the upper neck portion, the implant has a self-tapping thread, and the neck portion of the implant is provided with a porcelain-like coating. The surface energy, or xe2x80x9czeta potentialxe2x80x9d, and the surface tension of the implant are kept as low as possible. Materials used for the implants are preferably titanium, titanium-based alloys or porcelain-like substances. The depressions are preferably designed as systematically trapezoid grooves extending parallel to one another, said grooves being generated mechanically.
By virtue of the invention, an implant is now available which, while providing sound immediate postoperative primary stability, is distinguished, on account of improved osseointegration in terms of the biological union of the bone and the implant surface, by an accelerated and increased load-bearing capacity in terms of secondary anchoring.